Research Note

The masses of the neutron and donor star in the high-mass X-ray binary IGR J18027-2016^⋆

¹ Department of Physics & AstronomyThe Open University, Milton Keynes MK7 6AA, UK
e-mail: a.mason@open.ac.uk
² Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
³ School of Physics & Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA, UK
⁴ Division of Earth, Space & Environment, University of Glamorgan, Pontypridd, CF37 1DL, UK

Received: 2 June 2011
Accepted: 2 July 2011

Abstract

Aims. We report near-infrared observations of the supergiant donor to the eclipsing high mass X-ray binary pulsar IGR J18027-2016. We aim to determine its spectral type and measure its radial velocity curve and hence determine the stellar masses of the components.

Methods. ESO/VLT observations of the donor utilising the NIR spectrograph ISAAC were obtained in the H and K bands. The multi-epoch H band spectra were cross-correlated with RV templates in order to determine a radial solution for the system.

Results. The spectral type of the donor was confirmed as B0-1 I. The radial velocity curve constructed has a semi-amplitude of 23.8 ± 3.1 km s^-1. Combined with other measured system parameters, a dynamically determined neutron star mass of 1.4  ±  0.2–1.6  ±  0.3 M_⊙ is found. The mass range of the B0-B1 I donor was 18.6  ±  0.8–21.8  ±  2.4 M_⊙. These lower and upper limits were obtained under the assumption that the system is viewed edge-on (i = 90° with β = 0.89) for the lower limit and the donor fills its Roche lobe (β = 1 with i = 73.1°) for the upper limit respectively.